According to Wikipedia: 5222 TCP XMPP client connection (RFC 6120) Official 5223 TCP XMPP client connection over SSL Unofficial 5269 TCP XMPP server connection (RFC 6120) Official 5298 TCP UDP XMPP JEP-0174: Link-Local Messaging / Official XEP-0174: Serverless Messaging 8010 TCP XMPP File transfers Unofficial The port numbers are defined in RFC 6120 § 14.7.
contact list (in XMPP this is called a “roster”) Source: XMPP-IM – RFC 6121 § 1.3: Requirements
This is probably way too basic, but at least it’s technical: https://web.archive.org/web/20170916193014/http://www.adarshr.com/fun-with-xmpp-and-google-talk and the second part, https://web.archive.org/web/20171005104211/http://www.adarshr.com:80/fun-with-xmpp-and-google-talk-part-2 It explains what stanzas are, what types are available and stuff.